The present invention relates to improvements in conditioning of tobacco, and more particularly to improvements in a method of treating tobacco ribs prior to severing and drying. Still more particularly, the invention relates to improvements in a method of puffing (i.e., increasing the specific volume) of tobacco ribs (which are already separated from tobacco leaf laminae) prior to cutting and drying. Cutting and drying steps precede the admixture of comminuted ribs to shreds which are obtained by severing tobacco leaf laminae.
It is already known to increase the specific volume of tobacco ribs. The procedure is known as puffing. Such procedure normally involves heating the ribs so that the moisture therein evaporates and thereby increases the volume of the ribs. Heretofore known methods are not entirely satisfactory for a variety of reasons. Certain types of treatment affect the quality of ribs, and certain other types of treatment must be followed by expensive and time-consuming secondary treatment in order to relieve the expanded ribs of certain substances which might affect the taste of smokers' products and/or the health of the smoker. Furthermore, presently known puffing apparatus are complex and expensive. Still further, many presently known puffing methods do not result in sufficient expansion of ribs to warrant the outlay for machinery and energy input.
German Pat. No. 1,532,082 discloses a method of puffing tobacco ribs by contacting the ribs with a very hot gas stream for a short interval of time. The temperature of the gas stream is between 200.degree. and 370.degree. C.; therefore, the ribs are subjected to a very pronounced drying action. The moisture content of expanded ribs is so low that the ribs must be moistened prior to introduction into the rolling and comminuting apparatus. Moistening of expanded tobacco ribs invariably entails at least some reduction of specific volume. Moreover, the moistening step prior to severing is a time-consuming operation which is counterproductive as concerns the cost of treatment as well as the specific volume of the ribs. The energy requirements of apparatus which are used for the practice of the patented method are extremely high.
Rapid heating of moisture in the ribs can be achieved by resorting to a microwave heater. This is disclosed, for example, in British Pat. No. 947,280. The energy requirements of such heaters are high, and the heating action must be monitored with a high degree of accuracy in order to prevent abrupt rise of steam pressure in the ribs; this can result in bursting (actually in explosion) of the ribs.
Certain further proposals include soaking tobacco ribs in an organic fluid, such as Freon, and thereupon exposing the ribs to radiation in order to achieve rapid evaporation of organic fluid. The process is expensive because the organic fluid must be expelled from expanded ribs prior to further processing.
Commonly owned German Offenlegungsschrift No. 2,202,619 discloses a process which has found widespread acceptance in the industry. The process includes intensive moistening of ribs (e.g., soaking of the ribs in water) and simultaneous or subsequent heating so as to cause the ribs to swell. An advantage of such process is that the ribs are treated gently. However, the ribs must be subjected to a secondary treatment (rapid drying of their outermost layers and subsequent cooling) so as to confine the moisture in the inner strata.